DETROIT – All the Yankees have a back problem now – namely, their backs are up against a brick wall in a dark alley in Motown.

Just as many Yankees fans figured or feared, Randy Johnson came up small. For the second time in as many postseasons, he didn’t give his club a boost in Game 3 of the Division Series. Pitching with a herniated disk in his back, Johnson allowed five earned runs over 52/3 innings during the disastrous 6-0 defeat to Detroit.

Indeed, while the AL East champs didn’t make the plays behind him, the 43-year-old was outpitched by a former Yankees punchline in a battle of ornery, geriatric lefties. Now the Bombers must rely on No. 4 starter Jaret Wright – a significant drop-off in pay grade – simply to get home to Yankee Stadium and ace Chien-Ming Wang.

Asked if the series would be headed back to New York, Johnson answered, “I believe it will be.”

The game unraveled in the second when Detroit took a 3-0 lead on four well-placed, well-timed hits.

Carlos Guillen led off with a single to right and advanced on Ivan Rodriguez’s single to right that fell in front of Bobby Abreu. Sean Casey ripped the third consecutive single to right just under the glove of Robinson Cano (who didn’t dive), plating Guillen and moving Rodriguez to third just ahead of the tag attempt by Alex Rodriguez.

Detroit went up 2-0 when speedy Curtis Granderson beat out a fielder’s choice up the middle. Cano did well simply to stop the ball and shovel it to Derek Jeter, who couldn’t catch Granderson for the double play. Granderson stole second off Johnson’s pickoff move when Jason Giambi hesitated and threw too late to second. As luck would have it for the suddenly reeling Yanks, Placido Polanco punched an RBI single up the middle on the next pitch.

Battery-mate Jorge Posada was happy with Johnson’s performance.

“He was outstanding,” Posada said. “I’ve got to give him a lot of credit. He was a fighter. I’m really, really proud of what he did today.

“I’m really happy with what he did. I’ve got a lot of encouraging words. He really fought out there.”

The Tigers added two insurance runs after two outs in the sixth. Jeter leaped for Guillen’s liner, but the ball glanced off his glove for a single, and Rodriguez ripped an RBI double inside the third-base bag and just under the dive of Rodriguez. Casey’s RBI double to right-center sent Johnson to the showers and, possibly, the offseason.